Olivine Group of Minerals

In the earlier article we have discussed different groups of minerals, like Mica, Amphibole, Pyroxene, Quartz group of minerals. This is another important group of minerals, which include a series of minerals that crystallize in the orthorhombic system. These minerals range in composition from ”forsterite” Mg2 SiO4. The composition of common Olivine is (Mg,Fe)2 SiO4.

Olivine (General)

Properties of Olivine: (Mg, Fe)2 SiO4

  • Crystal System: Olivines have an Orthorhombic crystal system.
  • Fracture: Olivines are found in Conchoidal fracture.
  • Hardness: Olivines have a hardness of 6.5-7 on Moh’s scale.
  • Sp.gr: It has specific gravity equal to 3.27-4.37.
  • Lustre: Olivine group of minerals have a vitreous lustre.
  •  Colour: Minerals of olivine group have pale, yellow green or olive green.
  • Habit: Granular.
  • Streak: Olive green to brown.
  • Tenacity: Brittle
  • Cleavage: Poor/Indistinct.
  • Density: 4.46 g/cm3 (Measured)    4.45 g/cm3 (Calculated).

What physical properties of minerals include?

Occurrence: 

Olivine occurs mainly in the dark coloured igneous rocks such as gabbro, periodotite and basalt. The rock, dunite is made up almost wholly of olivine. Olivine alters very readity to serpentine.

Minerals of Olivine Species:

Dunite  Solid, grainy masses of Olivine. Usually classified as a rock.
Olivenoid Extraterrestrial form of Olivine found in meteorites.
Peridote Fe2Mg8O20Si5, Transparent green variety of Olivine that is used as a popular gemstone.
Calcio-olivine                                                             Ca2SiO4
Fayalite                                    Fe2+2SiO4
Forsterite                                              Mg2SiO4
Glaucochroite                                                          CaMn2+SiO4
Kirschsteinite                                                         CaFe2+SiO4
Laihunite                       (Fe2+0.50.5)Fe3+[SiO4]
Larnite                                    Ca2SiO4
Liebenbergite                                                                 Ni2SiO4
Monticellite                                                    CaMgSiO4
Tephroit                                            Mn2+2SiO4

Uses of Olivine Minerals:

  • Olivine is used in metallurgical process as a slag conditioner (A slag conditioner containing MgO, carbon or a filler and a binder is mixed and formed under pressure to produce aggregates which can have the form of a briquette. The slag conditioner is used to improve the operating performance and refractory life in steel melting furnaces).
  • Forsterite (a magnesium rich olivine) is added to blast furnaces to remove impurities from steel and to form a slag.
  • Olivine is used as refractory material, and casting sand, while making refractory bricks (ceramic bricks/ tiles). But usage of olivine as refractory material is not a cheap source, which is why it is gradually being replaced by other cheaper materials.
  • Olivine is resembles to ”peridote”, which is used in jewelry and has metaphysical importance. As peridote is expensive, therefore, Olivine is used as peridote substitutely.
  • Bricks made up of Olivine refractory material are used in construction of stoves and furnaces because of its high resistivity against heat and high temperatures.
  • Olivine refractory material is used in bricks to reduce the weathering caused by continuous heating and cooling of the walls of stoves.

Countries rich with Olivine Minerals:

Olivine is found abundantly in igneous rocks of following geographic regions;
  • Ultramafic intrusions (e.g., Norway, Germany);
  • Ophiolite complexes (e.g., Greece, Italy, Turkey);
  • Alpine peridotites (ophiolite or subcontinental mantle) emplaced along thrust faults (e.g., Italy, Spain);
  • Rift zones/basalts of mid-ocean ridges (e.g., Iceland);
  • Volcanic xenoliths (e.g., German Eifel and Kaiserstuhl, Iceland).
  • A melilite–olivine nephelinite lava flow occurring in Hamada, SW Japan.

 

 

 

 

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